JP3334138B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to air-fuel ratio sensor on the upstream side and the downstream side of the catalytic converter (herein, oxygen concentration sensor (O ₂ sensor)) is provided, the air-fuel ratio feedback by the O ₂ sensor on the upstream side The present invention relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control using a downstream O ₂ sensor in addition to control.

[0002]

2. Description of the Related Art In a simple air-fuel ratio feedback control (single O ₂ sensor system), an oxygen concentration detecting O
_Two places in the exhaust system close to the combustion chamber as possible sensors, i.e. are provided to the set portion of the exhaust manifold is upstream of the catalytic converter, to improve the control accuracy of the air-fuel ratio for variations in the output characteristic of the O ₂ sensor A problem has occurred. Such O ₂ component variation variation and the fuel injection valve and the output characteristics of the sensor, to compensate for time or secular change, a second O ₂ sensor disposed downstream of the catalytic converter, by the upstream O ₂ sensor There has already been proposed a double O ₂ sensor system for performing air / fuel ratio feedback control using a downstream O ₂ sensor in addition to air / fuel ratio feedback control (see Japanese Patent Application Laid-Open No. 61-234241). In this double O ₂ sensor system, although the O ₂ sensor provided on the downstream side of the catalytic converter has a lower response speed than the downstream O ₂ sensor, variation in output characteristics is small for the following reasons. Has advantages.

(1) Since the exhaust gas temperature is low downstream of the catalytic converter, there is little thermal effect. (2) Downstream of the catalytic converter, various poisons are trapped by the catalyst, so that the amount of poisoning of the downstream O ₂ sensor is small. (3) The exhaust gas is sufficiently mixed downstream of the catalytic converter, and the oxygen concentration in the exhaust gas is close to the equilibrium state.

[0004] Thus, as described above, the air-fuel ratio feedback control based on the outputs of the two O ₂ sensors (double O ₂ sensor system), the variations in the output characteristic of the upstream O ₂ sensor can be absorbed by the downstream O ₂ sensor . Actually, as shown in FIG. 11, in a single O ₂ sensor system, when the O ₂ sensor output characteristic deteriorates,
While the exhaust emission characteristics are directly affected, in the double O ₂ sensor system, even if the output characteristics of the upstream O ₂ sensor deteriorate, the exhaust emission characteristics do not deteriorate. That is, in the double O ₂ sensor system, the downstream O
Good exhaust emissions are guaranteed as long as the _two sensors maintain stable output characteristics.

The above-mentioned double O ₂ sensor system (Japanese Patent Application Laid-Open
In 61-234241 discloses), downstream O ₂ sensor in the air-fuel ratio feedback control constant as the skip amount RSR (RSL) a constant update rate ΔRS according to the output ([Delta] R
S ′), the air-fuel ratio correction coefficient FAF is calculated using the skip amount according to the output of the upstream O ₂ sensor, and the air-fuel ratio of the engine is adjusted according to the air-fuel ratio correction coefficient FAF. .

[0006]

However, this is not the case.
The constant update speed of the skip amount RSR (RSL)
A problem arises when updating is carried out. That is, three
The source catalyst is unburned in exhaust gas when the air-fuel ratio is stoichiometric.
Has a function to purify HC, CO and NOx well
You. Further, the three-way catalyst has a function of storing oxygen, so-called O
It has _two storage function, to the O ₂ storage function
Even if the air-fuel ratio slightly deviates from the stoichiometric air-fuel ratio, the exhaust gas
Unburned HC, CO and NOx in the fuel
You. In other words, when the air-fuel ratio becomes slightly lean,
Oxygen is deprived of NOx in the medium, and this oxygen
Stored in a medium. As a result, NOx is purified
Become. On the other hand, the air-fuel ratio becomes slightly rich
And the oxygen stored in the three-way catalyst converts unburned HC and CO
To convert unburned HC and CO as a result
Will be done.

[0007] Thus, the O ₂ storage function of the three-way catalyst
Even if the air-fuel ratio slightly deviates from the stoichiometric air-fuel ratio due to
Combustion HC, CO and NOx can be purified. This
, The higher the O ₂ storage capacity of the three-way catalyst, the more theoretical
Even if the deviation of the air-fuel ratio from the air-fuel ratio is large, the unburned HC,
CO and NOx are purified. 2 and 3
Te W1 is observed when a high O ₂ storage capability of the three-way catalyst
Indicates the air-fuel ratio range that can purify fuel HC, CO and NOx
are doing. On the other hand, the three-way catalyst when the three-way catalyst is deteriorated O ₂
Storage capacity decreases, resulting in unburned HC, CO and
The range of air-fuel ratio that can purify NOx and NOx becomes narrow. Figure 2 and
In FIG. 3, W2 indicates the air-fuel ratio range at this time.
You.

By the way, as described above, the air-fuel ratio
Skip amount RS which is a control constant of feedback correction coefficient
R is constantly updated at a constant update speed. this
Update speed is relatively fast to obtain good responsiveness
Set to degree. The solid line in FIG. 2 O ₂ strike the three-way catalyst
This indicates when the storage capacity is high.
When the ratio becomes richer than the air-fuel ratio range W1, the scan is started.
The tip amount RSR is reduced. The skip amount RSR is
When it is lowered, the air-fuel ratio gradually becomes leaner,
When the fuel ratio is leaner than the air-fuel ratio range W1, the
The kipping amount RSR is increased. On the other hand, the solid line in FIG.
Shows when the O ₂ storage capacity of the three-way catalyst is low
At this time, the air-fuel ratio is larger than the air-fuel ratio range W2.
The skip amount RSR decreases when the vehicle becomes rich
Can be When the skip amount RSR is reduced, the air-fuel ratio
Gradually becomes leaner, and the air-fuel ratio exceeds the air-fuel ratio range W2.
Also on the lean side, the skip amount RSR increases this time
Can be

As described above, when the air-fuel ratio is in the air-fuel ratio range W1 or W1.
When it exceeds 2, the air-fuel ratio is returned to the lean side. By the way, the sky
When the fuel ratio exceeds the air-fuel ratio range W1 or W2, the rich
The degree is much greater in FIG. 2 than in FIG.
High, so the air-fuel ratio has exceeded the air-fuel ratio range W1 or W2
Sometimes the case of FIG. 2 is much more than the case of FIG.
The amount of unburned HC and CO is discharged. That is,
Kip amount RSR is always updated at a constant update speed
A large amount of non when the O ₂ storage capability of the three-way catalyst is high when
When fuel HC and CO are emitted and at the same time exhaust odor is generated
The problem described above arises.

[0010]

[Means for Solving the Problems] To solve the above problems
In the present invention, as shown in the configuration diagram of the invention in FIG.
O provided in the engine exhaust passage _Two  Has storage function
Three-way catalyst, Installed in the engine exhaust passage upstream of the three-way catalyst
And an upstream air-fuel ratio sensor that detects the air-fuel ratio of the engine
When, Provided in the engine exhaust passage downstream of the three-way catalyst, the engine
A downstream air-fuel ratio sensor for detecting the air-fuel ratio of Upstream air-fuel
The air-fuel ratio detected by the ratio sensor becomes the stoichiometric air-fuel ratio.
Control means for controlling the air-fuel ratio feedback correction coefficient
When, The air-fuel ratio detected by the downstream air-fuel ratio sensor is theoretical
Control of the air-fuel ratio feedback correction coefficient so as to achieve the air-fuel ratio
Update that updates the constant at a predetermined update rate
Means, Fuel injection by air-fuel ratio feedback correction coefficient
Injection amount adjusting means for adjusting the injection amount, Deterioration of three-way catalyst
Means for determining the degree of deterioration of the catalyst for determining; Deterioration degree of three-way catalyst is small
In the case of a three-way catalyst,
Update speed calculating means for lowering the new speed; Has
You.

[0011]

[Action] When the degree of deterioration of the three-way catalyst is small, the feedback
Of the control constant of the lock correction coefficient, for example, the skip amount RSR.
The new speed is reduced as shown by the dashed line in FIG. FIG.
Update of the skip amount RSR as indicated by the solid line in FIG.
When the speed is high, the air-fuel ratio exceeds the air-fuel ratio range W1
Later, after becoming richer, the air-fuel ratio moves toward the lean side.
Will be returned. Thus, the air-fuel ratio is lower than the upper limit of the air-fuel ratio range W1.
And the air-fuel ratio is in the air-fuel ratio range W
Because rich time is longer than the upper limit of 1,
An amount of unburned HC and CO is discharged, and an exhaust odor is generated.
On the other hand, as shown by a broken line in FIG.
When the update speed of the amount RSR is reduced, the air-fuel ratio falls within the air-fuel ratio range.
It does not become richer beyond the upper limit of the box W1. Therefore
Emission of a large amount of unburned HC and CO is suppressed and exhaust
Odor generation can be suppressed.

[0012]

FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention. In FIG.
An air flow meter 3 is provided in an intake passage 2 of the engine body 1. The air flow meter 3 directly measures the amount of intake air, and for example, incorporates a potentiometer and generates an output signal of an analog voltage proportional to the amount of intake air. This output signal is provided to the A / D converter 101 with a built-in multiplexer of the control circuit 10. Distributor 4 has its axis converted to, for example, crank angle.
A crank angle sensor 5 that generates a reference position detection pulse signal every 20 ° and a crank angle sensor 6 that generates a reference position detection pulse signal every 30 ° in terms of a crank angle are provided. The pulse signals of the crank angle sensors 5 and 6 are supplied to an input / output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to an interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from a fuel supply system to an intake port for each cylinder. The water jacket 8 of the cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of the cooling water. The water temperature sensor 9 generates an analog voltage electric signal corresponding to the cooling water temperature THW. This output is also supplied to the A / D converter 101.

[0014] exhaust system downstream of the exhaust manifold 11, three toxic components HC in the exhaust gas, CO, catalytic converter 12 housing the three-way catalyst for simultaneously purifying NO _x is provided. A first O ₂ sensor 13 is provided in the exhaust manifold 11, that is, on the upstream side of the catalytic converter 12,
A second O ₂ sensor 15 is provided in the exhaust pipe 14 on the downstream side of the catalytic converter 12. The O ₂ sensors 13 and 15 generate an electric signal corresponding to the concentration of the oxygen component in the exhaust gas. That, O ₂ sensor 13, 15 depending on whether the lean side or the rich side with respect to the air-fuel ratio is the stoichiometric air-fuel ratio, Ru generates a different output voltage at the output of the A / D converter 101 of the control circuit 10.

The control circuit 10 is configured as, for example, a microcomputer, and is provided with a ROM 104, a RAM 105, a backup RAM 106, a clock generation circuit 107, and the like in addition to the A / D converter 101, the input / output interface 102, and the CPU 103. The throttle valve 16 of the intake passage 2 is provided with an idle switch 17 for generating a signal LL indicating whether or not the throttle valve 16 is fully closed. This idle state output signal LL is supplied to the input / output interface 102 of the control circuit 10.

Numeral 18 denotes a secondary air introduction control valve which supplies secondary air to the exhaust pipe 11 at the time of deceleration or idling.
This is to reduce C and CO emissions. Further, in the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110 are for controlling the fuel injection valve 7. That is, when the fuel injection amount TAU is calculated in a routine described later, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts a clock signal (not shown) and its borrow-out terminal finally becomes "1" level, the flip-flop 109 is set and the driving circuit is set.
110 stops the energization of the fuel injection valve 7. That is, the fuel injection valve 7 is energized by the above-described fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1.

Note that the CPU 103 generates an interrupt after the A / D conversion of the A / D converter 101 is completed.
2, when a pulse signal from the crank angle sensor 6 is received, and so on. The intake air amount data Q and the cooling water temperature data THW of the air flow sensor 3 are fetched by an A / D conversion routine executed at a predetermined time or every predetermined crank angle, and stored in a predetermined area of the RAM 105. That is, the data Q and THW in the RAM 105 are updated every predetermined time. The rotation speed data _Ne is output from the crank angle sensor 6.
And is stored in a predetermined area of the RAM 105 by an interrupt at every 30 ° CA.

The operation of the control circuit shown in FIG. 4 will be described below.
FIGS. 5 and 6 show a first air-fuel ratio feedback control routine for calculating an air-fuel ratio correction coefficient FAF based on the output of the upstream O ₂ sensor 13, which is executed every predetermined time, for example, every 4 ms. In step 501, the air-fuel ratio of the closed loop by the upstream O ₂ sensor 13 (feedback) condition is determined whether or not satisfied. For example, when the coolant temperature is below a predetermined value, during engine start-up, during post-increase start, during warming increase in power boosting, in OTP boost for the catalyst overheat prevention, the output signal of the upstream O ₂ sensor 13 is once Is not inverted,
During the fuel cut or the like, the closed loop condition is not satisfied in any case, and in other cases, the closed loop condition is satisfied. If the closed loop condition is not satisfied, the process proceeds directly to step 530. Note that the air-fuel ratio correction coefficient FAF may be set to 1.0. On the other hand,
If the closed loop condition is satisfied, the process proceeds to step 502.

In step 502, the output V ₁ of the upstream O ₂ sensor 13 is A / D converted and taken in.
_1, it is determined whether or not the comparison voltage V _R1 for example 0.45V or less, that is, the air-fuel ratio is determined whether rich or lean. If lean (V ₁ ≦ V _R1), the delay counter CDLY is to determine positive or not at step 504, and 0 to CDLY at step 505 if CDLY> 0, the process proceeds to step 506.
In step 506, the delay counter CDLY is decremented by one,
In steps 507 and 508, the delay counter CDLY is set to the minimum value T.
Guard with DL. In this case, when the delay counter CDLY reaches the minimum value TDL, in step 509, the air-fuel ratio flag F1 is set to "0" (lean). Note that the minimum value TDL is a lean delay state for maintaining the judgment that the output is the rich state even when the output of the upstream O ₂ sensor 13 changes from rich to lean, and is defined by a negative value. You. On the other hand, if rich (V ₁ > V _R1 ), it is determined in step 510 whether or not the delay counter CDLY is negative.
If CDLY <0, CDLY is set to 0 in step 511, and the flow advances to step 512. In step 512, the delay counter CD
LY is incremented by 1 and the delay counter is set in steps 513 and 514.
Guard CDLY with maximum value TDR. In this case, when the delay counter CDLY reaches the maximum value TDR, the air-fuel ratio flag F1 is set to "1" (rich) in step 515. Note that the maximum value TDR is a rich delay state for maintaining the determination that the output of the upstream O ₂ sensor 13 is in a lean state even when there is a change from lean to rich, and is defined as a positive value. You.

In step 516, it is determined whether or not the sign of the air-fuel ratio flag F1 has been inverted, that is, whether or not the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is inverted, it is determined in step 517 whether the air-fuel ratio is inverted from rich to lean or from lean to rich, based on the value of the air-fuel ratio flag F1. If the inversion is from rich to lean, in step 518, the rich skip amount RSR is read from the backup RAM 106 and is increased in a skipping manner as FAF ← FAF + RSR. Conversely, if the inversion is from lean to rich, the flow proceeds to step 519. The lean skip amount RSL is read from the backup RAM 106, and FAF ← FAF-RSL is reduced in a skip manner. That is, skip processing is performed.

If it is determined in step 516 that the sign of the air-fuel ratio flag F1 has not been inverted, an integration process is performed in steps 520, 521, and 522. That is, at step 520, F1 =
It is determined whether or not “0”. If F1 = “0” (lean), in step 521, it is set as FAF ← FAF + KIR.
If “1” (rich), then at step 522, FAF ← F
AF-KIL. Here, the integration constants KIR and KIL are set sufficiently smaller than the skip amounts RSR and RSL.
KIR (KIL) <RSR (RSL). Therefore, step 521 gradually increases the fuel injection amount in the lean state (F1 = "0"), and step 522 gradually reduces the fuel injection amount in the rich state (F1 = "1").

Further, skip 523-
528 indicates the number of inversions C of the output V ₁ of the upstream O ₂ sensor 13.
Count M. That is, in step 523, the intake air amount Q / N per rotation is within the predetermined range (A <Q / N <B).
Whether, in step 524, the rotational speed N, it is determined whether or not within a predetermined range _{(C <N e <D)} , in step 525, whether the downstream air-fuel ratio feedback control flag XSFB is "1" or That is, it is determined whether or not the air-fuel ratio feedback condition by the downstream O ₂ sensor 15 is satisfied. As a result, the engine is in a stable state (A <Q / N <B and C
<N <D), and only when the air-fuel ratio feedback control condition by the downstream O ₂ sensor 15 is satisfied, the routine proceeds to step 526, where the counter CM is incremented by one or +1. Guard at the maximum value. Otherwise, the process proceeds to step 528 to clear the counter CM.

Next, the air-fuel ratio correction coefficient FAF calculated in steps 518, 519, 521, 522 is guarded in step 529 at a minimum value, for example, 0.8, and a maximum value, for example, 0.8.
Guarded in 1.2. Thus, if the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason, the air-fuel ratio of the engine is controlled with these maximum or minimum values to prevent over-rich or over-lean.

The FAF calculated as described above is stored in the RAM 105, and the loop ends at step 530. FIG. 7 is a timing chart for supplementarily explaining the operation according to the flowcharts of FIGS. When the rich / lean discrimination air-fuel ratio signal A / F is obtained from the output of the upstream O ₂ sensor 13 as shown in FIG.
As shown in FIG. 7B, the count is performed in the rich state and the count is reduced in the lean state. As a result,
As shown in FIG. 7C, the air-fuel ratio signal A subjected to the delay processing
/ F '(corresponding to the flag F1). For example,
Also the air-fuel ratio signal A / F is changed from lean to rich at time t _1, the air-fuel ratio signal A / F which is delayed processed 'rich at time t ₂ after being held lean only the rich delay time TDR Changes to Even the air-fuel ratio signal A / F at time t ₃ is changed from rich to lean, the delayed air-fuel-fuel ratio signal A / F 'is the time after being held rich only equivalent lean delay time (-TDL) t It changes to lean at ₄ . However Invert empty-fuel ratio signal A / F 'is the time t _5, t _6, a period shorter than the rich delay time TDR as the t _7, takes time delay counter CDLY reaches the maximum value TDR, the result, the air-fuel ratio signal a / F after the delay is reversed at time t _8. That is, the air-fuel ratio signal A / F 'after the delay processing is more stable than the air-fuel ratio signal A / F before the delay processing. In this way, the air-fuel ratio correction coefficient FAF shown in FIG. 7D is obtained based on the stable air-fuel ratio signal A / F 'after the delay processing.

Next, the second air-fuel ratio feedback control by the downstream O ₂ sensor 15 will be described. As the second air-fuel ratio feedback control, the skip amounts RSR and RSL as the first air-fuel ratio feedback control constant, the integration constant
KIR, KIL, there are a system for delay time TDR, TDL, or the comparison voltage V _R1 of the output V ₁ of the upstream O ₂ sensor 13 to the variable, and a system for introducing a second air-fuel ratio correction coefficient FAF2 is.

For example, if the rich skip amount RSR is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean skip amount RSL is reduced, the control air-fuel ratio can be shifted to the rich side. Is increased, the control air-fuel ratio can shift to the lean side, and the control air-fuel ratio can shift to the lean side even if the rich skip amount RSR is reduced. Therefore, the air-fuel ratio can be controlled by correcting the rich skip amount RSL according to the output of the downstream O ₂ sensor 15. Also, the rich integration constant KIR
Is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean integration constant KIL is reduced, the control air-fuel ratio can be shifted to the rich side. On the other hand, if the lean integration constant KIL is increased, the control air-fuel ratio is shifted to the lean side. Side, and
Even if the rich integration constant KIR is reduced, the control air-fuel ratio can be shifted to the lean side. Therefore, the rich integration constant KIR and the lean integration constant K are determined according to the output of the downstream O ₂ sensor 15.
The air-fuel ratio can be controlled by correcting IL. Increase the rich delay time TDR or increase the lean delay time (-TD
If L) is set small, the control air-fuel ratio can shift to the rich side. Conversely, if the lean delay time (-TDL) is set large or the rich delay time (TDR) is set small, the control air-fuel ratio shifts to the lean side. Can be migrated. That is, the air-fuel ratio can be controlled by correcting the delay time TDR, the TDL in accordance with the output of the downstream O ₂ sensor 15. Furthermore, it shifts the control air-fuel ratio by increasing the comparison voltage V _R1 to the rich side, also, possible shifts the control air-fuel ratio by decreasing the reference voltage V _R1 to the lean side. Accordingly, the air-fuel ratio can be controlled by correcting the reference voltage V _R1 in accordance with the output of the downstream O ₂ sensor 15.

These skip amounts, integration constants, delay times,
Making the comparison voltage variable by the downstream O ₂ sensor has its own advantages. For example, the delay time allows very fine adjustment of the air-fuel ratio, and the skip amount is
Control with good response is possible without lengthening the feedback cycle of the air-fuel ratio like the delay time. Therefore, these variable amounts can be used in combination of two or more.

Next, a description will be given double O ₂ sensor system in which the skip amounts are braking <br/> control constants of the air-fuel ratio feedback correction coefficient to the variable. FIGS. 8 and 9 show a second air-fuel ratio feedback control routine based on the output of the downstream O ₂ sensor 15, which is executed every predetermined time, for example, every 512 ms. In steps 801 to 806, the downstream O ₂ sensor 15
That by the closed-loop it is determined whether or not all conditions are satisfied.
For example, when the cooling water temperature THW is equal to or lower than a predetermined value (for example, 70 ° C.) (Step 802), in addition to the closed loop condition not being satisfied by the upstream O ₂ sensor 13 (Step 801), the throttle valve 16 is fully closed (LL = “LL”). 1 ") (step 803),
The rotation speed _Ne , the vehicle speed, the signal LL of the idle switch 17,
When the secondary air is not introduced based on the cooling water temperature THW or the like (step 804), when the load is light (Q / _Ne <X
₁₎ (step 805), when the downstream O ₂ sensor 15 is not activated (step 806) and the closed loop condition is not satisfied, otherwise it is a closed loop condition is satisfied. If the closed loop condition is not satisfied, the routine proceeds to step 807, where the air-fuel ratio feedback control execution flag XSFB is reset (“0”),
If the closed loop condition is satisfied, the routine proceeds to step 808, where the air-fuel ratio feedback control execution flag XSFB is set (" 1 "). The air-fuel ratio feedback control execution flag XSFB is used in step 525 of FIG.

The flow in step 808 includes steps 809 to
Continue to 827. In step 809, the rich skip amount RS
Catalytic converter converts integral speed RSKI out of R update speed
The calculation is performed according to the degree of deterioration of the 12-way catalyst. In other words, the number of reversals CS of the downstream O ₂ sensor 15 and the upstream O 2
_Since the ratio CS / CM to the number of reversals CM of the _two sensors indicates the degree of deterioration of the three-way catalyst, the ratio CS / CM shown in step 809 is used.
The following function is stored in the ROM 104 in advance, and the integration speed RSK
Interpolate I. As shown in step 809, if the degree of deterioration CS / CM is small, the integral speed RSKI is reduced,
If the degree of deterioration CS / CM is large, the integral speed RSKI is increased.

The calculation of the integral speed at step 809 is executed only when the number of reversals CM of the upstream O ₂ sensor is equal to or greater than a predetermined value. When the CM does not reach the predetermined value, Alternatively, the integrated speed RSKI calculated when the CM reaches a predetermined value at a previous stage may be used. Similarly, the catalyst deterioration degree can be estimated from other parameters. For example, the larger the accumulated traveling distance of the engine and the accumulated intake air amount, the larger the deterioration degree. The speed RSKI may be obtained.

[0031] At step 810, it receives the output V ₂ of the downstream O ₂ sensor 15 is converted A / D, V _2, it is determined whether or not the comparison voltage V _R2 eg 0.55V or less at step 811, that is, It is determined whether the air-fuel ratio is rich or lean. The comparison voltage V _R2 is calculated from the comparison voltage V _R1 of the output of the upstream O ₂ sensor 13 in consideration of, for example, the difference in output characteristics due to the influence of raw gas and the deterioration rate at the upstream and downstream of the catalytic converter 12. Although set high, this setting is optional. As a result, if V ₂ ≦ VR ₂ (lean),
Proceeds to step 812 to reset the air-fuel ratio flag F2 ( "0"), also, if V _2> V _R2 (rich), the process proceeds to step 813, and sets the air-fuel ratio flag F2 ( "1").

In step 814, it is determined whether or not the sign of the air-fuel ratio flag F2 has been inverted, that is, whether or not the air-fuel ratio downstream of the catalyst has been inverted. If the air-fuel ratio has been inverted, it is determined in step 815 whether the air-fuel ratio is inverted from rich to lean or from lean to rich, based on the value of the air-fuel ratio flag F2. If the inversion is from rich to lean, the rich skip amount RSR is read from the backup RAM 106 in step 816 and RSR is increased in a skipping manner to RSR + RSRS. Conversely, if the inversion is from lean to rich, step 817 is executed. Then, RSR ← RSR−RSRS is reduced in a skip manner. That is, skip processing is performed.

If it is determined in step 814 that the sign of the air-fuel ratio flag F2 has not been inverted, integration processing is performed in steps 818, 819, and 820. That is, at step 818, F2 =
It is determined whether or not “0”. If F2 = “0” (lean), at step 819, RSR ← RSR + RSKI is set.
If “1” (rich), at step 820 RSR ← R
SR-RSKI. Here, the integral constant RSKI is the skip amount RS
It is set sufficiently smaller than RS, that is, RSKI <RS
RS. Therefore, step 819 is performed in a lean state (F1 =
In step 820, the rich skip amount RSR is gradually decreased in the rich state (F2 = “1”).

Further, every time skip processing is performed,
825 indicates the number of inversions C of the output V ₂ of the downstream O ₂ sensor 15
Count S. That is, in step 82 1, the intake air quantity Q / N per revolution within a predetermined range (A <Q / N <B )
Whether, in step 822, the rotational speed N _e is determined whether or not within a predetermined range _{(C <N e <D)} . As a result,
When the engine is in a stable state (A <Q / N <B and C <N <D) only, the process proceeds to step 82 3, the counter CS +1
Counts up to the guard at the maximum value counter CS at step 82 4. Otherwise, go to step 825,
Clear the counter CS. Then, the process proceeds to step 826.

In step 826, the RSR is set to the maximum value MAX.
(= 7.5%) and guard the RSR to the minimum value MIN (= 2.
5%). Note that the minimum value MIN is a value at a level at which the transient followability is not impaired, and the maximum value MA
X is a level value at which drivability does not deteriorate due to air-fuel ratio fluctuation. In step 827, the lean skip amount RSL is set to RSL ← 10% −RSR. That is, RSR + RSL = 10%.

In step 928, the skip amounts RSR and RSL are stored in the backup RAM 106. And step 829
Ends this routine. FIG. 10 shows an injection amount calculation routine that is executed at a predetermined crank angle, for example, 360 ° CA. In step 1001, calculates the basic injection amount TAUP reads the intake air amount data Q and the rotational velocity data N _e from the RAM 105. For example, TAUP ← α · Q / N _e (α is a constant). In step 1002, the final injection amount TAU is set to TAU ←
Calculate by TAUP ・ FAF ・ β + γ. Here, β and γ are correction amounts determined by other operation state parameters. Next, at step 1003, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. Then, in step 1004, this routine ends.

As described above, when the time corresponding to the injection amount TAU elapses, the flip-flop 109 is reset by the borrow-out signal of the down counter 108, and the fuel injection ends. Further, each first air-fuel ratio feedback control is 4 ms, also the second air-fuel ratio feedback control is performed for each 512ms, the air-fuel ratio feedback control is mainly controlled by good responsiveness upstream O ₂ sensor This is for performing the control by the downstream O ₂ sensor having poor response.

A double O ₂ sensor system that corrects other control constants in the air-fuel ratio feedback control by the upstream O ₂ sensor, for example, a delay time, an integration constant, and the like by the output of the downstream O ₂ sensor, The present invention can also be applied to a double O ₂ sensor system that introduces a second air-fuel ratio correction coefficient. Controllability can be improved by simultaneously controlling two of the skip amount, the delay time, and the integration constant. Further, it is also possible to fix one of the skip amounts RSR and RSL and to make only the other variable,
It is also possible to fix one of them and make only the other variable, or to fix one of the rich integration constant KIR and the lean integration constant KIL and make the other variable.

As the intake air amount sensor, a Karman vortex sensor, a heat wire sensor or the like can be used instead of the air flow meter. Further, in the above-described embodiment, the fuel injection amount is calculated according to the intake air amount and the engine speed, but the fuel injection amount is calculated according to the intake air pressure and the engine speed, or the throttle valve opening and the engine speed. The fuel injection amount may be calculated.

Further, in the above embodiment, the internal combustion engine in which the fuel injection amount is controlled by the fuel injection valve is shown. However, the present invention can be applied to a carburetor type internal combustion engine. For example, an electric air control valve (E
(ACV) to control the air-fuel ratio by adjusting the intake air amount of the engine, and to adjust the air bleed amount of the carburetor by the electric bleed air control valve to introduce air into the main passage and the slow passage. Controlling the air-fuel ratio, sent to the exhaust system of the engine 2
The present invention can be applied to a device for adjusting the amount of secondary air, and the like. In this case, the basic injection amount TA in step 1001 in FIG.
The basic fuel injection amount equivalent to UP is determined by the carburetor itself, that is, determined according to the intake pipe negative pressure and the engine speed according to the intake air amount, and supplied at step 1002 corresponding to the final fuel injection amount TAU. The air amount is calculated.

Further, in the above-described embodiment, the O ₂ sensor is used as the air-fuel ratio sensor, but a CO sensor, a lean mixture sensor, or the like may be used. In particular, when a TiO ₂ sensor is used as the upstream air-fuel ratio sensor, control responsiveness is improved, and overcorrection due to the output of the downstream air-fuel ratio sensor can be prevented. Further, although the above-described embodiment is constituted by a microcomputer, that is, a digital circuit, it may be constituted by an analog circuit.

[0042]

According to the present invention, if the O ₂ storage capacity of the three-way catalyst is high,
A large amount of unburned HC and CO are emitted during the operation, and exhaust odor is generated
Can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is a timing chart showing the operation of the present invention.

FIG. 3 is a timing chart showing the operation of the present invention.

FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention.

FIG. 5 is a flowchart illustrating the operation of the control circuit of FIG. 4;

FIG. 6 is a flowchart for explaining the operation of the control circuit of FIG. 4;

FIG. 7 is a timing chart for supplementarily explaining the flowcharts of FIGS. 5 and 6;

FIG. 8 is a flowchart illustrating the operation of the control circuit of FIG. 4;

FIG. 9 is a flowchart illustrating the operation of the control circuit of FIG. 4;

FIG. 10 is a flowchart illustrating an operation of the control circuit of FIG. 4;

FIG. 11 is an emission characteristic diagram illustrating a single O ₂ sensor system and a double O ₂ sensor system.

[Explanation of symbols]

1 ... engine body 2 ... air flow meter 4 ... distributor 5,6 ... crank angle sensor 10 ... control circuit 12 ... catalytic converter 13 ... upstream O ₂ sensor 15 ... downstream O ₂ sensor 17 ... idle switch

Claims (1)

(57) [Claims] 1. A three-way catalyst having an O ₂ storage function provided in an engine exhaust passage , and an upstream side provided in an engine exhaust passage upstream of the three-way catalyst and detecting an air-fuel ratio of the engine. An air-fuel ratio sensor, a downstream air-fuel ratio sensor provided in an engine exhaust passage downstream of the three-way catalyst and detecting an air-fuel ratio of the engine, and an air-fuel ratio detected by the upstream air-fuel ratio sensor are theoretically determined.
Control the air-fuel ratio feedback correction coefficient to achieve the air-fuel ratio.
Control means for controlling the air-fuel ratio detected by the downstream air-fuel ratio sensor.
Control of the air-fuel ratio feedback correction coefficient so as to achieve the air-fuel ratio
Update that updates the constant at a predetermined update rate
Means and a fuel injection amount according to the air-fuel ratio feedback correction coefficient.
An injection quantity adjusting means for adjusting a catalyst deterioration degree determination means for determining the deterioration degree of the three way catalyst, said compared to when a large degree of deterioration of the three way catalyst when the deterioration degree of the three-way catalyst is small updates air-fuel ratio control system for an internal combustion engine provided with slow Kusuru update rate calculating means, the speed.